1. Field of the Invention
The present invention relates to a small-size wide angle photographic lens having a refractive power arrangement of a so-called telephoto type.
2. Description of the Prior Art
With the recent trend of smaller and thinner cameras, lenses used therefor have been desired to have a small distance from the front of the lens to the image plane.
To this end, there is one method in which the focal length of the lens is made short to provide a wide angle lens. It is also known to be advantageous to provide a so-called telephoto type in which a convergent positive lens system is arranged in the front group whereas a divergent negative lens system is arranged in the rear group. However, the telephoto type is originally advantageous in structure as a lens of a narrow angle of view. If the wide angle is provided while maintaining a large spacing between the convergent lens system in the front group and the divergent lens system in the rear group necessary for decreasing the telephoto ratio, both the front and rear groups abnormally increase in lens aperture, deteriorating the aberration accordingly. Therefore, it has been difficult to increase the aperture ratio and to increase the angle of view.
Small-size wide angle lenses of the telephoto type as described above have been often found in well known publications, which have the rear group in the form of a negative meniscus single lens in which convex surface is directed toward the image. In these lenses, however, the spacing between the front group and the rear group is large, and therefore, the diameter of the lens in the rear group is large. Thus, the increase in aperture ratio and the increase in angle of view give rise to the deterioration of aberration. For example, there have been proposed wherein the aperture ratio is merely 1:3.5 with respect to the angle of the view 63.degree. (Japanese Patent Publication No. 50248/81) and wherein the structure similar to the former is provided and the aperture ratio is 1:2.8 which is brighter with the result that the angle of view becomes narrow, 59.4.degree., which involves difficulties in coma aberration, chromatic aberration of magnification, difference due to color of coma aberration, etc. (Japanese Patent application Laid-Open No. 75612/81) and the like. These proposals are not yet sufficient in terms of performance.
In addition, these divergent lenses in the rear group comprise a meniscus negative lens having a deep concave surface towards the object, and therefore, said concave surface adversely affects the coma aberration. To cope with this, proposals have been recently made in which aspherical configuration is used in the lens of the rear group to improve the coma aberration. However, these proposals involve various problems in manufacture, and it is apparent to be advantageous in that the lens may be constructed only by the spherical configuration.